<html>
  <head>
    <style>
      .box {
        width: 10px;
        height: 10px;
        border: 1px solid red;
        margin: 2px;
        padding: 2px;
        background: blue;
      }

      #borderBox {
        box-sizing: border-box;
      }

      #contentBox {
        box-sizing: content-box;
      }
      #threeangle {
        height: 10px;
        width: 10px;
        background-color: gray;
        border-right: 15px solid orange;
        border-left: 15px solid blue;

        /* border-color: orange blue red green; */
      }
    </style>
  </head>
  <body>
    <div>请问下面两个 div 元素，蓝色区域的宽高各是多少像素？</div>
    <div id="borderBox" class="box"></div>
    <div id="contentBox" class="box"></div>
    <div id="threeangle"></div>
  </body>
</html>